Novel method for crystal defect analysis of laser drilled TSVs

Beyond doubt through silicon vias (TSVs) will pave the way for 3D interconnects and therefore initiate what is widely considered as the next revolution for electronic packaging and hetero system integration. During the last years the manufacturing of through silicon vias has been intensely studied in Advanced Packaging and starts industrial commercialization at the moment. Due to its low cost and flexibility laser drilling is a favored technology for the backend of line via fabrication. However, little is published or known on effects of this via manufacturing like crystal defects and sub-surface damage. In this context the paper at hand proposes white beam synchrotron X-ray topography as a non-destructive method to reasonably complement existing characterization techniques. This method is well established in crystallographic research, however, it has never been used before to assess the sub-surface damage of laser drilled TSVs. The basic principle of white beam synchrotron X-ray topography (SXRT), its resulting images and their evaluation will be explained and the three used set-ups described in detail. The paper compares the use of standard X-ray films to use of high-resolution films that require long-term exposures but allow higher accuracy. The effectiveness of SXRT is verified by analyzing laser drilled TSVs, which have been manufactured with normal (ns), short (ps) and ultra-short (fs) pulse width lasers. This first-time comparison of the sub-surface damage clearly identifies that femtosecond lasers are superior. The methodology prepared for this research can be easily generalized and applied to continuing investigations and hence is highly suited to optimize the packaging density and TSV manufacturing technologies.